This application is the US national phase of PCT application PCT/EP98/01321 filed Mar. 6, 1998 with a claim to the priority of German application 197 23 513.1 filed Jun. 5, 1997.
The invention relates to a knife drum for machines for cross-cutting webs, in particular paper or cardboard webs, having a generally cylindrical support body of a fiber-reinforced material on whose surface is secured at least one holder for a blade extending the length of the drum.
Cross-cutting machines for producing sheets of paper or cardboard have as is known two knife drums rotatably supported one above the other in a machine frame and having blades that engage each other for cutting in order to transversely cut through the continuous web. In order that paper or cardboard webs of considerable width can be cut with high accuracy and at high production speeds, the knife drums must meet numerous requirements:
The maximum resistance to torsional and bending deformation must be achieved with minimal mass. The knife drum must have the highest possible self damping and must be resistant to mechanical and chemical damage. In order to cut thick paper or cardboard webs it is necessary to conduct considerable cutting forces over large surfaces via the blade into the surface of the knife drum without there being any unacceptable radial deformations in the region where the blades are secured.
German patent 4,321,163 describes a knife drum of this type with a cylindrical drum body that is formed of a plastic tube that is made of carbon-fiber reinforced epoxy resin. A metallic blade holder is fixed on the plastic tube. The carbon fibers are imbedded as a continuous helix in the body of the plastic tube. carbon-fiber reinforced plastic segments are set between the blade holders with their carbon fibers extending generally parallel to the rotation axis of the plastic tube.
It is an object of the invention to produce a blade drum that has improved resistance to bending and torsional stresses relative to its volume.
This object is achieved according to the invention in that the support body is formed of two concentrically interfitted tubes of fiber-reinforced material, that the fibers of the inner tube are wound across one another at positive and negative angles of 30xc2x0 to 60xc2x0, preferably 45xc2x0, to the rotation axis of the support body, that the fibers of the outer tube are wound at a positive and/or negative angle of less than 30xc2x0, preferably less that 10xc2x0, to the rotation axis of the support body, and that the blade holder is fixed in a groove extending the full length of the drum and cut into the outer surface of the outer tube by a chip-removing procedure, in particular by milling.
The blade drum according to the invention has two separate layers of which the inner layer is substantially responsible for torsional stiffness and the outer layer is substantially responsible for bending stiffness. Both layers are made of a fiber-reinforced material whose fibers are imbedded in the body.